It has been observed that both endotoxin and non-endotoxin components from gram-negative bacteria can induce bone resorption (BR). The present grant proposes to explore this observation in detail and has two major objectives. The first objective is the isolation of the BR active component from Actinobacillus actinomycetemcomitans (Aa) strains. The white-type polysaccharide (WPS) from AaY4 was partially purified by ion exchange chromatography, HPLC, thin layer chromatography and high voltage electrophoresis. Chemical analyses demonstrated that the WPS contained no detectable lipid, glucosamine or phosphate but only the polysaccharide moiety of endotoxin. This WPS stimulated bone resorption in both the rat calvaria and isolated chick osteoclast system. Efforts are continuing to purify the active fractions in larger amounts. The second objective of the project deals with the mechanism of in vitro BR. Experiments with isolated chick osteoclasts suggested that endotoxin and WPS may act indirectly through a second cell, i.e. lymphocytes or macrophages. To test this possibility osteoclasts will be co-cultivated with secondary cell populations and treated with endotoxin or WPS. If these materials work via a second messenger, then enhanced resorption may be detected utilizing this dual culture system.